Pulsator

ABSTRACT

A pulsator has two valve devices (1, 2), each of which is adapted to alternately subject a pulsation space to two different pressures. In order to avoid the two valve devices (1, 2) from disturbing each other during the alternations between the two pressures a third valve device (23) is arranged, for closing communication between one of the valve devices and the lower one of said two pressures, when the other valve device is operated to alternate the pressure in the pulsation space from the lower one to the higher one of said two pressures.

BACKGROUND OF THE INVENTION

The present invention relates to a pulsator, comprising first and secondvalve devices, each of which has a pulsation outlet, a pressure inlet tobe connected to a first source of pressure generating a first pressure,and a pressure outlet to be connected to a second source of pressuregenerating a second pressure, which is lower than said first pressure.Means is provided for adjusting each valve device for alternatelyconnecting the pulsation outlet of the valve device to said first sourceof pressure via the pressure inlet of the valve device and to saidsecond source of pressure via the pressure outlet of the valve device.

DESCRIPTION OF THE PRIOR ART

There is a known pulsator of this kind which among other things isutilized in milking machines for providing cyclic pressure alternationin the pulsation spaces of the teat cups, i.e. the spaces formed in theteat cups between the walls of the teat cups and the liners mounted inthe teat cups. In this case, four teat cups are usually connected inpairs to each one of the two pulsation outlets of the first and secondvalve devices in the known pulsator, and said first source of pressureis constituted by atmosphere, while said second source of pressure isconstituted by a source of subatmospheric pressure.

The known pulsator is operated with the two valve devices offset inphase relative to each other, which means that when vacuum(subatmospheric pressure) prevails in the pulsation spaces of one of thepairs of teat cups, atmospheric pressure can prevail in the pulsationspaces of the other pair of teat cups. However, during each pulsationcycle comprising a period of atmospheric pressure and a period ofvacuum, the period of atmospheric pressure normally has a shorterduration than the period of vacuum. During a certain time of eachpulsation cycle, vacuum therefore prevails simultaneously in thepulsation spaces of all of the four teat cups. This has the consequencethat when the pulsation outlet of one of the valve devices communicateswith the source of subatmospheric pressure and the other valve device isoperated by the adjustment means to adjust the pulsation outlet fromcommunication with atmosphere to communication with the source ofsubatmospheric pressure, for a short moment atmosphere can alsocommunicate with the pulsation outlet of said one valve device via thenecessary conduit connections between the two valve devices and thesource of subatmospheric pressure. During said short moment atmosphericpressure thus occurs in the pulsation spaces of the pair of teat cupsconnected to said one valve device, which is felt by a cow being milkedas unpleasant pressure impacts against her teats.

Of course, it would be possible to avoid occurrence of such unpleasantpressure impacts if each valve device were constructed such that duringeach alternation operation, the pulsation outlet of the valve device iskept closed, when the adjustment means adjusts the pulsation outlet fromconnection with the pressure inlet (atmospheric pressure) to connectionwith the pressure outlet (subatmospheric pressure). However, valvedevices constructed in this way would substantially increase the priceof the pulsator.

The intensity of said pressure impacts could also be reduced so that thecows would feel the impacts less unpleasant, if the alternationoperation of the valve devices could take place in a faster rate.However, this would require complicated valve devices, probablyincluding servo systems, which would lead to too expensive pulsators.

In milking pulsators it is known to arrange two non-return valves in theconnections between the two pressure outlets of the valve devices andthe source of subatmospheric pressure to eliminate said pressure impactsor at least reduce their intensity. During the adjustment of one of thetwo valve devices for alternating the pulsation outlet from connectionwith the pressure inlet, which communicates with atmosphere, toconnection with the pressure outlet, the non-return valve between thesource of subatmospheric pressure and the pressure outlet of the othervalve device will close the resulted flow of air. Such an arrangement ofnon-return valves has certain drawbacks, however. Thus, if eachnon-return valve would be self-closing by means of for instance aspring, the non-return valve would give rise to a pressure dropproportional to the occurring self-closing force. Such a pressure dropwould disturb the desired level of vacuum in the pulsation spaces of theteat cups, whereby the milking operation would be jeopardized.

On the other hand, if each non-return valve would not be self-closing, avolume of air would have to flow momentarily through the non-returnvalve in order to create a sufficient pressure difference across thenon-return valve to close the latter. Such a momentary flow of air wouldalso give rise to non-desirable pressure impacts against the cows' teatsas described above, though of not quite such a strong intensity as thatof pulsators without non-return valves.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a simple andinexpensive pulsator, which eliminates momentary pressure impacts in thepulsation outlets, when subatmospheric pressure prevails in any of thepulsation outlets during operation.

This object is obtained by means of a pulsator of the kind initiallystated, which mainly is characterized by a third valve device having avalve housing, which forms a chamber, a first inlet to the chamber,connected to the pressure outlet of the first valve device, a secondinlet to the chamber connected to the pressure outlet of the secondvalve device, first and second valve seats extending around respectiveopenings of the first and second inlets in the chamber, and an outlet inthe chamber to be connected to said second source of pressure, and avalve member, which is displaceable in the chamber between a firstposition, at which the valve member abuts sealingly against the firstvalve seat, and a second position, at which the valve member abutssealingly against the second valve seat.

Suitably, the first and second valve seats of the valve housing faceeach other, which has the advantage that the valve member only needs toperform a short transversal movement to alternate between said first andsecond positions.

Preferably, the valve member is freely movable in the chamber betweensaid first and second positions, whereby the required force to move thevalve member can be minimized.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a pulsator in accordance withthe present invention; and

FIG. 2 is a schematic representation of the pulsator of FIG. 1 inanother adjustment.

The pulsator shown in FIGS. 1 and 2 comprises two similar valve devices1 and 2, each of which is designed as a conventionalelectro-magnetically controlled three-way valve. Thus, the valve device1 comprises a valve housing 3 with a chamber 4, an outlet 5 from thechamber 4, a valve seat 6, which surrounds the opening of the outlet 5in the chamber 4, an inlet 7 to the chamber 4, a valve seat 8, whichsurrounds the opening of the inlet 7 in the chamber 4, and a pulsationoutlet 9 from the chamber 4. A valve member 10 is situated in thechamber 4 and is provided with a valve shaft 12 extending through theinlet 7. The valve shaft 12, which is magnetic, extends further througha coil 11. By activating the coil 11 with an applied voltage the valvemember 10 can be displaced to abut sealingly against one of the valveseats 6 and 8.

Analogous to the valve device 1 the valve device 2 comprises a valvehousing 13 with a chamber 14, an outlet 15, a valve seat 16, whichsurrounds the outlet 15, an inlet 17, a valve seat 18, which surroundsthe inlet 17, and a pulsation outlet 19. A valve member 20 in thechamber 14 has a valve shaft 21 extending through the inlet 17 and acoil 22.

A third valve device 23 comprises a valve housing 24 with a chamber 25,an inlet 26 to the chamber 25, a valve seat 27, which surrounds theopening of the inlet 26 in the chamber 25, an inlet 28, which issituated in front of the inlet 26, a valve seat 29, which surrounds theopening of the inlet 28 in the chamber 25 and faces the valve seat 27,and an outlet 30 from the chamber 25.

In the chamber 25 there is a sheet shaped light valve member 31, whichis freely movable in the chamber 25 between a first position, at whichthe valve member 31 seals against the valve seat 27, and a secondposition, at which the valve member 31 seals against the valve seat 29.(The valve member 31 may also have other shapes, such as that of aball).

The outlets 5 and 15 are connected to the inlets 26 and 28,respectively, while the inlets 7 and 17 communicate directly withatmosphere.

The pulsator according to FIGS. 1 and 2 is operated in the followingmanner when for instance using it in milking machines:

The pulsation outlets 9 and 19 are connected to the pulsation spaces oftwo pairs of teat cups and the outlet 30 is connected to a source ofsubatmospheric pressure. With the valve devices 1, 2 and 23 in theadjustments shown in FIG. 1, vacuum prevails in the pulsation spaces inall of the four teat cups. When for instance the coil 22 is activatedfor adjusting the valve member 20 to seal against the valve seat 16, sothat atmospheric pressure will prevail in the pulsation spaces which areconnected to the pulsation outlet 19, atmosphere will communicate for ashort moment with the inlet 28 via the inlet 17, the chamber 14 and theoutlet 15 during the displacement of the valve member 20 towards thevalve seat 16 (FIG. 2). Since the pressure in the inlet 28 consequentlyincreases a pressure difference occurs across the valve member 31, whichresults in that the valve member 31 is pushed through the chamber 25 toabut sealingly against the valve seat 27. Thus, any increase in pressuredoes not occur in the pulsation outlet 9, whereby neither any pressureimpacts occur in the evacuated pulsation spaces, which are connected tothe pulsation outlet 9.

Since the period of atmospheric pressure has shorter duration than thevacuum period during each pulsation cycle, the valve member 20 isdisplaced back to the valve seat 18 before the valve member 10 isdisplaced from the valve seat 8. First thereafter the valve member 10 isdisplaced towards the valve seat 6, which results in that the valvemember 31 is pushed back to abut sealingly against the valve seat 29.When the period of atmospheric pressure has passed for the pulsationspaces which are connected to the pulsation outlet 9, the valve member10 is displaced back to the valve seat 8, whereby the pulsator againassumes the condition shown in FIG. 1.

I claim:
 1. In a pulsator comprising first and second valve devices,each of said first and second valve devices having a pulsation outlet, apressure inlet to be connected to a first source of pressure forgenerating a first pressure, and a pressure outlet to be connected to asecond source of pressure for generating a second pressure, said secondpressure being lower than said first pressure, said pulsator furthercomprising means for adjusting each of said first and second valvedevices for alternately connecting the pulsation outlet of each saidvalve device to said first source of pressure via the respective inletof the valve device and to said second source of pressure via therespective pressure outlet of the valve device, wherein the improvementcomprises a third valve device having a valve housing forming a chamber,a first inlet to said chamber connected to the pressure outlet of thefirst valve device, a second inlet to said chamber connected to thepressure outlet of the second valve device, first and second valve seatsextending around respective openings of the first and second inlets insaid chamber, an outlet from said chamber connected to said secondsource of pressure, and a valve member which is displaceable in thechamber between a first position at which the valve member abutssealingly against the first valve seat, and second position, at whichthe valve member abuts sealingly against the second valve seat.
 2. Apulsator according to claim 1, wherein said first and second valve seatsof said housing face each other in the chamber.
 3. A pulsator accordingto claim 1, wherein said valve member is freely movable in the chamberbetween said first and second positions.
 4. A pulsator according toclaim 2, wherein said valve member is freely movable in the chamberbetween said first and second positions.